Preheat your oven to 350°F (175°C) and grease a 9-inch loaf pan.

In a large mixing bowl, combine melted unsalted butter, brown sugar, and granulated sugar, whisk until smooth.

Mix in the sour cream, then add the eggs one at a time, stirring well after each addition. Incorporate vanilla extract and mashed bananas.

In another bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon. Gradually fold this into the wet mixture.

Pour the batter into the prepared loaf pan and bake for 45 to 55 minutes. Check for doneness at the 40-minute mark.

Let the banana bread cool in the pan for 10-15 minutes before transferring to a wire rack.